Determining String Design for an Inverter - Revision history

Marcin: /* PV String Design Prompt */

2026-04-12T23:08:46Z

PV String Design Prompt

← Older revision		Revision as of 23:08, 12 April 2026
Line 13:		Line 13:
	= PV String Design Prompt =		= PV String Design Prompt =

	Design the optimal PV string configuration for a solar inverter system.
			'''Design the optimal PV string configuration for a solar inverter system.''' - https://chatgpt.com/share/69dc215e-4594-83ea-b517-04446f495815

	== Goal ==		== Goal ==

Marcin: /* Full AI Prompt */

2026-04-12T23:07:35Z

Full AI Prompt

← Older revision		Revision as of 23:07, 12 April 2026
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	*For the total number of strings, check max power of PV and make sure it is within the rated power input rating of the inverter.		*For the total number of strings, check max power of PV and make sure it is within the rated power input rating of the inverter.

	~~=Full AI Prompt=~~
	= PV String Design Prompt =		= PV String Design Prompt =

Marcin: /* Summary */

2026-04-12T23:07:25Z

Summary

← Older revision		Revision as of 23:07, 12 April 2026
Line 6:		Line 6:
	The procedure, if you want to verify the AI result, is:		The procedure, if you want to verify the AI result, is:
	*Essentially, take Voc, and compare to max voltage of inverter (typically 500 VDC)		*Essentially, take Voc, and compare to max voltage of inverter (typically 500 VDC)
	*Correct for low temperature.		*Correct for low temperature - Voc increase ≈ 3% per 10°C below 25°C. Such as 13.5% for -20C [https://chatgpt.com/share/69dc215e-4594-83ea-b517-04446f495815]
	*Determine max panels that fit within max voltage		*Determine max panels that fit within max voltage
	*Use max current of input to determine if you should parallel strings		*Use max current of input to determine if you should parallel strings

Marcin at 22:59, 12 April 2026

2026-04-12T22:59:40Z

@@ Line 1: / Line 1: @@
 Go to AI and ask:
@@ Line 9: / Line 10: @@
 *Use max current of input to determine if you should parallel strings
 *For the total number of strings, check max power of PV and make sure it is within the rated power input rating of the inverter.

Marcin at 22:57, 12 April 2026

2026-04-12T22:57:03Z

Show changes

Marcin: Created page with "{| class="wikitable" ! Step ! What to check ! Formula / Rule ! What it determines ! Notes |- | 1 | Gather panel data | Need: Voc, Vmp, Isc, Imp, panel wattage, Voc temperature coefficient | Inputs for all later calculations | Use the actual module datasheet, not only the sales listing. |- | 2 | Gather inverter PV input data | Need: max DC voltage, MPPT voltage range, max input current per MPPT/input, max short-circuit current if listed, max PV wattage per MPPT, total m..."

2026-04-12T22:50:59Z

Created page with "{| class="wikitable" ! Step ! What to check ! Formula / Rule ! What it determines ! Notes |- | 1 | Gather panel data | Need: Voc, Vmp, Isc, Imp, panel wattage, Voc temperature coefficient | Inputs for all later calculations | Use the actual module datasheet, not only the sales listing. |- | 2 | Gather inverter PV input data | Need: max DC voltage, MPPT voltage range, max input current per MPPT/input, max short-circuit current if listed, max PV wattage per MPPT, total m..."

New page

{| class="wikitable"
! Step
! What to check
! Formula / Rule
! What it determines
! Notes

|-
| 1
| Gather panel data
| Need: Voc, Vmp, Isc, Imp, panel wattage, Voc temperature coefficient
| Inputs for all later calculations
| Use the actual module datasheet, not only the sales listing.

|-
| 2
| Gather inverter PV input data
| Need: max DC voltage, MPPT voltage range, max input current per MPPT/input, max short-circuit current if listed, max PV wattage per MPPT, total max PV wattage
| Inputs for inverter-side limits
| Treat each MPPT/input separately unless the manual clearly says inputs are internally paralleled.

|-
| 3
| Choose design minimum temperature
| Use lowest expected cell or ambient temperature for conservative design
| Needed for maximum string voltage
| Cold increases panel voltage, so this is a safety-critical step.

|-
| 4
| Correct panel Voc for cold weather
| Voc,cold = Voc,STC × [1 + |temp coefficient of Voc| × (25°C - Tmin)]
| Real worst-case open-circuit voltage per panel
| If coefficient is given in %/°C, convert to decimal first. Example: 0.28%/°C = 0.0028/°C.

|-
| 5
| Determine maximum panels in series
| Max series panels = floor(inverter max DC voltage / Voc,cold)
| Maximum safe string length
| This is based on Voc, not Vmp.

|-
| 6
| Check MPPT operating window
| String Vmp = number of series panels × panel Vmp
| Confirms whether inverter can track the string
| String Vmp should fall within the inverter MPPT voltage range under normal operating conditions.

|-
| 7
| Check low-end MPPT startup
| String Vmp should be comfortably above the inverter MPPT minimum
| Confirms inverter will wake up and track well
| Designing too close to the MPPT minimum can cause poor performance in hot weather.

|-
| 8
| Check high-end MPPT limit
| String Vmp should stay below the inverter MPPT maximum
| Confirms normal operating voltage is usable
| This is different from absolute max DC voltage, which is checked with Voc.

|-
| 9
| Determine current of one string
| For one series string: string current is approximately panel Imp for operating current, and panel Isc for fault/current-limit checks
| Current contribution of one string
| Series adds voltage, not current.

|-
| 10
| Determine maximum parallel strings by operating current
| Max parallel strings by Imp = floor(inverter max input current per MPPT / panel Imp)
| Maximum number of strings per input from current limit
| This usually controls how many strings can be placed on one MPPT.

|-
| 11
| Determine maximum parallel strings by short-circuit current
| Max parallel strings by Isc = floor(inverter max short-circuit input current per MPPT / panel Isc)
| Safety check on parallel string count
| Use this if the inverter datasheet lists max PV short-circuit current. If not listed, at minimum respect the operating current limit.

|-
| 12
| Determine maximum parallel strings by wattage per MPPT
| Max strings by MPPT power = floor(max PV watts per MPPT / string wattage)
| Maximum strings per input from power rating
| String wattage = series panel count × panel wattage.

|-
| 13
| Determine maximum parallel strings by total inverter PV wattage
| Total allowed strings = floor(total max PV watts / string wattage)
| Whole-inverter cap on string count
| After finding total allowed strings, distribute them across MPPTs without exceeding per-input limits.

|-
| 14
| Final allowable strings per input
| Allowable strings per input = smallest result from Step 10, Step 11, and Step 12
| Final answer for each MPPT/input
| Then confirm the total across all inputs also satisfies Step 13.

|-
| 15
| Check symmetry and MPPT grouping
| Keep strings on the same MPPT electrically similar
| Proper inverter tracking
| Same orientation, tilt, shading profile, and module type should generally be grouped on the same MPPT.

|-
| 16
| Add design margin
| Stay somewhat below absolute limits where practical
| Better reliability and fewer edge-case failures
| Do not design right at the 500 V maximum or current maximum unless the manufacturer explicitly supports it and conditions are well characterized.

|-
| 17
| Final design output
| Report: panels per string, strings per MPPT, total strings, total DC watts
| Complete PV stringing layout
| Also report cold-corrected string Voc and nominal string Vmp.

|-
| 18
| Final rule summary
| Strings per input = minimum of current limit, short-circuit current limit, per-MPPT wattage limit, and any manufacturer string-count limit
| One-line decision rule
| Series count is set by voltage; parallel count is set mainly by current and power.

|}

== Compressed procedure ==

{| class="wikitable"
! Question
! Use
! Main formula

|-
| How many panels can go in one string?
| Voltage limit
| floor(max DC voltage / cold-corrected Voc)

|-
| How many strings can go on one input?
| Current and MPPT power limit
| minimum of floor(max input current / Imp), floor(max short-circuit current / Isc), floor(max PV watts per MPPT / string watts)

|-
| How many strings can go on the whole inverter?
| Total PV power limit
| floor(total max PV watts / string watts)

|}

== Core principle ==

{| class="wikitable"
! Quantity
! Series connection does this
! Parallel connection does this

|-
| Voltage
| Adds
| Stays about the same

|-
| Current
| Stays about the same
| Adds

|-
| Main design constraint
| Voc and Vmp
| Imp, Isc, and input wattage

|}

== Example template ==

{| class="wikitable"
! Item
! Value
! Result

|-
| Panel Voc
|
|

|-
| Panel Vmp
|
|

|-
| Panel Imp
|
|

|-
| Panel Isc
|
|

|-
| Panel wattage
|
|

|-
| Voc temp coefficient
|
|

|-
| Inverter max DC voltage
|
|

|-
| Inverter MPPT range
|
|

|-
| Inverter max input current per MPPT
|
|

|-
| Inverter max short-circuit current per MPPT
|
|

|-
| Inverter max PV watts per MPPT
|
|

|-
| Inverter total max PV watts
|
|

|-
| Minimum design temperature
|
|

|-
| Calculated max panels in series
|
|

|-
| Calculated max strings per input
|
|

|-
| Calculated max total strings
|
|

|-
| Final design
|
|

|}